Imaging optical module designed to be associated with an optical semiconductor component and method of fabricating same

ABSTRACT

An imaging optical module is designed to be placed in front of an optical image sensor of a semiconductor component. The module includes at least one element which has a refractive index that varies between its optical axis and its periphery, over at least an annular part and/or over its central part. The element may be a tablet in front of the semiconductor sensor or a lens in front of the semiconductor sensor. The direction of variation in refractive index may be oppositely oriented with respect to the table and lens.

PRIORITY CLAIM

The present application is a translation of and claims priority fromFrench Application for Patent No. 07 52665 of the same title filed Jan.15, 2007, the disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to the general field of cameras and, moreparticularly, the field of semiconductor components including opticalimage sensors in front of which are installed imaging optical modulesfor projecting images onto these optical image sensors.

2. Description of Related Art

It is currently known that such optical modules can comprise a glasslens, a glass tablet placed between the lens and the sensor and adiaphragm between the lens and the tablet. It is also known that suchelements are advantageously stacked one on top of the other.

Nevertheless, there is currently a limit to the increase in the numberof pixels forming the optical sensors because the captured images becomeblurred and/or have less contrast.

There is a need to improve the resolution power and/or the contrast ofthe imaging optical modules associated with optical semiconductorcomponents, with a view to being able to increase the sharpness and/orthe contrast of the images captured by the semiconductor componentscurrently available and/or increase the number of pixels forming theoptical image sensors of the components, without reducing the sharpnessand/or the contrast of the captured images.

SUMMARY OF THE INVENTION

In an embodiment an imaging optical module is designed to be placed infront of an optical image sensor of a semiconductor component andthrough which an image is projected towards this optical image sensor.

This module can comprise at least one element which has a refractiveindex that varies between its optical axis and its periphery, over atleast an annular part and/or over its central part.

According to a variant, the refractive index of said element canadvantageously vary in one direction.

According to an embodiment, the imaging optical module comprises atleast one element which has a refractive index that varies between itsoptical axis or its central part and its periphery.

According to an embodiment, the imaging optical module comprises atleast a first element including a tablet with parallel faces and asecond element including an optical lens, at least one of these elementshaving a refractive index that varies between its optical axis and itsperiphery, over at least an annular area.

Said elements can have refractive indices that vary in the reversedirection between their optical axis or their central part and theirperiphery.

The refractive index of said tablet can increase between its opticalaxis or its central part and its periphery.

The refractive index of said lens can decrease between its optical axisor its central part and its periphery.

In accordance with another embodiment, a method is presented forfabricating an imaging optical element designed to be placed in front ofan optical image sensor of a semiconductor component and through whichan image is projected towards this optical image sensor.

This method comprises the following step: doping the material formingsaid element with ions suitable for modifying the refractive index ofthis element, such that this index varies between its optical axis orits central part and its periphery, over at least an annular area.

The method comprises, previously, the following step: doping thematerial forming said element with different ions.

The method comprises, previously, a step for additionally doping thematerial forming said element with preliminary doping ions or with otherions.

In one aspect, the element is made of glass and the doping ions arechosen from the group of sodium, potassium, lithium, silver, cesium andthallium ions.

The method comprises the following step: doping with thallium ions anelement made of glass previously doped with sodium ions.

The element can comprise a tablet.

According to an aspect, the method comprises the following step: dopingwith sodium ions an element made of glass previously doped with thalliumions.

Said element can comprise a lens.

The method comprises the following steps: forming on said element a maskhaving at least one annular aperture and/or a central aperture; dopingthe material forming this element through this mask; and removing saidmask.

Another embodiment is a method of fabricating imaging optical elementsdesigned to be placed in front of optical image sensors of semiconductorcomponents and through which images are projected towards these opticalimage sensors.

This method comprises the following steps: taking a wafer; makingcrossed grooves, which may be rectilinear, in a front face of said waferso as to form protruding blocks; forming a mask covering the rear faceof said wafer, the end faces of said blocks and the bottom of saidgrooves; doping with ions the material forming said wafer through saidmask, radially producing a doping of each of said blocks; and removingsaid mask; such that the refractive index of each block varies betweenits optical axis or its central part and its periphery.

Alternatively, the method comprises the following steps: taking a wafer;forming on a front face of said wafer a mask comprising, over areas ofthis front face, a central aperture and/or at least one annularaperture; forming a mask covering the rear face of said wafer; dopingwith ions the material forming said wafer through said mask; andremoving said masks; such that the refractive index of each part of saidwafer corresponding to said areas varies between its optical axis or itscentral part and its periphery.

Another embodiment comprises a wafer with parallel faces comprising amultiplicity of parts respectively comprising imaging optical tabletsdesigned to be placed in front of optical image sensors of semiconductorcomponents and through which images are projected towards these opticalimage sensors, each tablet having a refractive index that varies betweenits optical axis and its periphery, over at least an annular part and/orover its central part.

Another embodiment comprises a wafer comprising a multiplicity of partsrespectively forming imaging optical lenses designed to be placed infront of optical image sensors of semiconductor components and throughwhich images are projected towards these optical image sensors, eachoptical lens having a refractive index that varies between its opticalaxis and its periphery, over at least an annular part and/or over itscentral part.

Another embodiment comprises an imaging optical device comprising saidwafer with tablets and said wafer with lenses, joined together so thatsaid optical elements and said optical lenses are placed one on top ofthe other and form optical modules.

Another embodiment is a method of fabricating optical semiconductordevices. This method comprises the following steps: joining togethersaid wafer with tablets and said wafer with lenses so that said opticalelements and said optical lenses are placed one on top of the other andcomprise imaging optical modules; joining to said wafer with tablets awafer comprising a multiplicity of parts respectively comprisingsemiconductor components with optical image sensors so that said imagingoptical modules and said semiconductor components are placed one on topof the other; and sawing said joined wafers so as to cut out amultiplicity of semiconductor devices with optical image sensorsrespectively comprising a semiconductor component and an imaging opticalmodule.

Another embodiment is an optical semiconductor package. This opticalsemiconductor comprises: a semiconductor component comprising an opticalimage sensor on its front face, an imaging optical module placed infront of the optical image sensor of the semiconductor component andthrough which an image is projected towards this optical image sensor,said imaging optical module comprising at least one element which has arefractive index varying between its optical axis and its periphery,over at least an annular part and/or over its central part.

The refractive index of said element of said package varies in onedirection.

Said imaging optical module of said package comprises at least a firstelement comprising a tablet with parallel faces placed in front of thesemiconductor component and a second element comprising an optical lensplaced in front of said tablet, a diaphragm being inserted between saidtablet and said lens, at least one of these elements having a refractiveindex varying between its optical axis and its periphery, over at leastan annular area.

Said elements of said package have refractive indices varying in thereverse direction between their optical axis or their central part andtheir periphery.

The refractive index of said tablet of said package may increase betweenits optical axis or its central part and its periphery.

The refractive index of said lens of said package may decrease betweenits optical axis or its central part and its periphery.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from studying elementsand optical modules designed to be placed in front of an optical sensorof a semiconductor component, and their fabrication methods, describedby way of non-limiting examples and illustrated by the drawings inwhich:

FIG. 1 represents an axial cross section of a package containing anoptical module;

FIG. 2 represents a perspective view of a wafer of tablets;

FIG. 3 represents a cross section of a portion of the wafer of FIG. 2,according to a first processing step;

FIG. 4 represents a top view of the portion of FIG. 3;

FIG. 5 represents the portion of FIG. 3, according to a subsequentprocessing step;

FIG. 6 represents the portion of FIG. 3, after a final processing step;

FIG. 7 represents a cross section of a portion of the wafer of FIG. 2,according to a first step of another process;

FIG. 8 represents a top view of the portion of FIG. 7;

FIG. 9 represents the portion of FIG. 7, according to a subsequentprocessing step;

FIG. 10 represents the portion of FIG. 7, according to a subsequentprocessing step;

FIG. 11 represents the portion of FIG. 3, after a final processing step;

FIG. 12 represents a cross-sectional view of a wafer of optical lenses;

FIG. 13 represents a cross section of a portion of the wafer of FIG. 12,according to a first processing step;

FIG. 14 represents a top view of the portion of FIG. 13;

FIG. 15 represents the portion of FIG. 12, according to a subsequentprocessing step;

FIG. 16 represents the portion of FIG. 12, after a final processingstep;

FIG. 17 represents an assembly of the portions of FIGS. 11 and 16; and

FIG. 18 represents a mounting of the assembly of FIG. 17 on a wafer ofsemiconductor components.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, it can be seen that an optical semiconductorpackage 1 is represented, comprising a stack 2 comprising asemiconductor component 3 which has on its front face 4 an optical imagesensor 5, and an imaging optical module 6.

According to the present description, an optical image sensor is able tocapture one or more images of a scene occurring in front of saidpackage. Such an image sensor normally comprises a multiplicity ofindividual photodiodes respectively transforming a stream of photonsinto an electrical signal, forming pixels.

According to the present description, an imaging optical module 6 is anoptical unit through which an optical image sensor sees said scene.

This imaging optical module 6 comprises a transparent tablet 7,preferably made of glass, of which the rear face 8 and the front face 9are parallel, a diaphragm 10 and a front convergent lens 11, preferablymade of glass, of which the rear face 12 is flat and the front face 13is convex, for example hemispherical, the diaphragm 10 being interposedbetween the front face 9 of the tablet 7 and the rear face 12 of thelens 11.

The optical image sensor 5, the transparent tablet 7, the diaphragm 10and the lens 11 have the same optical axis 14.

The stack 2 is housed axially in a through passage 15 of an opaquecasing 16, the lens passing through an internal shoulder in thispassage, forming a front end stop for the tablet 7. The rear face 18 ofthe semiconductor component 3 is provided with balls 19 for externalelectrical connection.

The tablet 7 has a refractive index that varies between its optical axisand its periphery, over at least an annular part and/or over its centralpart. In the example described, the refractive index of the tablet 7progressively increases substantially between the optical axis 14 or itscentral part and its periphery.

The lens 11 has a refractive index that varies between its optical axisand its periphery, over at least an annular part and/or over its centralpart. In the example described, the refractive index of the lens 11progressively decreases substantially between the optical axis 14 or itscentral part and its periphery.

To obtain the tablet 7 and the lens 11 having such variable refractiveindices, the glass can be doped appropriately with metal ions chosenfrom, for example, sodium (Na⁺), potassium (K⁺), lithium (Li⁺), silver(Ag⁺), cesium (Cs⁺) and thallium (Tl⁺) ions.

There now follows a description, with examples, of how a multiplicity oftablets 7 can be fabricated.

FIG. 2 shows how it is possible to begin with a large-size wafer 20 madeof glass. This wafer is, for example, previously doped substantiallyuniformly throughout for example with thallium ions (Tl⁺), for exampleby dipping it in a thallium nitrate (TlNO₃) bath and under the effect ofan accelerating electrical field oriented in the direction of itsthickness.

FIGS. 3 to 6 illustrate a first method.

As FIGS. 3 and 4 show, opposing masks 23 and 24, corresponding to eachother in the direction of thickness of the wafer, are produced in theform of films, for example by deposition, on the faces 21 and 22 of thewafer 20. These masks are such that, on parts 7 a of the wafer 20intended to subsequently form tablets 7, a central aperture 25 and anannular aperture 26 are provided, these parts 7 a being distributed in asquare matrix.

Then, as shown by FIG. 5, the wafer 20 is doped, through the masks 23and 24, for example with sodium ions (Na⁺), for example by dipping it ina bath of sodium nitrate (NaNO₃) and under the effect of an acceleratingelectrical field oriented in the direction of its thickness.

The masks 23 and 24 and the above doping are adapted so that the densityof Na⁺ ions contained in the material decreases substantially betweenthe axis 14 of each part 7 a or its central part and its periphery.

Then, as shown in FIG. 6, the masks 23 and 24 are removed.

The result of the treatment described above is that the refractive indexof each part 7 a of the wafer 20 increases between respectively itsoptical axis 14 or its central part and its periphery, in a radialgradient determined by the radial variation of the density of the dopingions in the glass.

FIGS. 7 to 11 illustrate a second way of treating the wafer 20.

As shown by FIGS. 7 and 8, crossed grooves 25 are formed in the frontface 21 of the wafer 20, so as to form blocks 7 b protruding relative tothe small remaining thickness, these blocks being intended tosubsequently form tablets 7 and being distributed in a square matrix.The crossed grooves 25 can be produced so as to form protruding blocksof any form, for example square or circular.

Then, as shown in FIG. 9, films are produced, for example by deposition,to form a mask 26 which covers the end faces 27 of the blocks 7 b andthe bottom 28 of the crossed grooves 25 and a mask 29 which completelycovers the rear face 22 of the wafer 20. Thus, the sides of the blocks 7b are uncovered.

Then, as shown in FIG. 10, the blocks 7 b of the wafer 20 are radiallydoped, via their uncovered sides, for example with thallium ions (Tl⁺),for example by dipping the wafer 20 in a bath of thallium nitrate(TlNO₃).

The above doping is adapted so that the density of Tl⁺ ions contained inthe material increases substantially between the periphery of each block7 b and its central part or its axis 14.

Then, as shown in FIG. 11, the masks 26 and 29 are removed.

The result of this is that the refractive index of each block 7 b of thewafer 20 increases between its optical axis 14 or its central part andits periphery, in a radial gradient determined by the radial variationof the density of the doping ions in the glass.

According to another variant, it would, additionally, be possible todope the crust of the peripheral part of the blocks 7 a with sodium ions(Na⁺), so as to slightly reduce the refractive index in the extremeperipheral part of the blocks 7 a, relative to the above increase.

With reference to FIGS. 12 to 16, there now follows a description, byway of example, of how to fabricate a multiplicity of lenses 11.

As shown in FIG. 12, it is possible to begin with a large-size wafer 30made of glass, which presents a disk 31 on a front face 31 a of whichlenses 11 are formed, protruding on this disk, spaced and distributedaccording to a square matrix, the lenses being, for example,hemispherical.

There then follows a preliminary doping, overall, of the wafer 30, forexample using thallium ions (Tl⁺), for example by dipping it in a bathof thallium nitrate (TlNO₃).

Then, as shown in FIGS. 13 and 14, films are produced, for example bydeposition, to form a mask 32 which covers the flat face of the wafer 30and a multiplicity of masks 33 which partially cover the convex faces 13of the lenses 11, each mask 33 comprising a round central part 33 a andspaced-apart annular parts 33 b leaving uncovered between them annularareas starting from this round central part.

Then, as shown in FIG. 15, the wafer 30 is doped, for example withsodium ions (Na⁺), for example by dipping it in a bath of sodium nitrate(NaNO₃).

The above doping is adapted so that the density of Na⁺ ions contained inthe material increases substantially between the central part or theaxis 14 and the periphery of each lens 11.

Then, as shown in FIG. 16, the masks 32 and 33 are removed.

The result of this is that the refractive index of each lens 11 of thewafer 30 decreases between its optical axis 14 or its central part andits periphery, in a radial gradient determined by the radial variationof the density of the doping ions in the glass.

There now follows a description of how a multiplicity of imaging opticalmodules 6 can be fabricated from wafers 20 and 30 treated as describedpreviously.

A film 34 is produced, for example by deposition, on the face 22 of thewafer 20, providing openings 10 a centered on the optical axes 14 of theparts 7 a in the case of the first variant or of the blocks 7 b in thecase of the second variant, so as to form a multiplicity of diaphragms10.

Then, the flat face of the wafer 30 is joined to the layer 34, via atransparent glue, so that the optical axes of the parts 7 a in the caseof the first variant or of the blocks 7 b in the case of the secondvariant correspond to the optical axes of the lenses 11.

There is thus obtained, as shown in FIG. 17, a wafer 35 comprising amultiplicity of imaging optical modules 6 distributed in a squarematrix.

Having a wafer 37 comprising a multiplicity of semiconductor components3 distributed in a square matrix, this wafer 37 is joined to the face 21of the wafer 20 included in the wafer 35 so that the optical axes of theimaging optical modules 6 correspond to the optical axes of the sensors5 of the semiconductor components 3.

There is thus obtained, as shown in FIG. 18, a wafer 38 comprising amultiplicity of stacks 2.

Then, this wafer 38 is sawn so as to separate and cut out each of thestacks 2, each consisting of a semiconductor component 3 and an imagingoptical module 6, as described with reference to FIG. 1.

As an example, on the one hand, the tablet 7 can have a width of between3 and 5 mm and a thickness of between 1 and 3 mm and on the other handthe lens 11 can have a radius of between 1.3 and 1.7 mm and a thicknessof between 0.5 and 1.5 mm.

In addition, the variation of the refractive index of the tablet 7 and,conversely, of the lens 11, between its central part and its peripheralpart can, as a percentage, be between 4 and 9%. Purely as an example,this variation can take the form of a parabola, the tip of which wouldbe approximately at half the radius of the tablet or of the lens.

The present invention is not limited to the examples described. It alsoapplies to any stacking of any number of lenses and/or of tablets,separated or not by air, containing at least one element having anon-zero index gradient, radial in particular.

Although preferred embodiments of the method and apparatus of thepresent invention have been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it will be understoodthat the invention is not limited to the embodiments disclosed, but iscapable of numerous rearrangements, modifications and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

1. An imaging optical module designed for placement in front of anoptical image sensor of a semiconductor component and through which animage is projected towards this optical image sensor, comprising atleast one element having a refractive index that varies between itsoptical axis and its periphery, over at least an annular part.
 2. Themodule according to claim 1, wherein the refractive index of saidelement varies in one direction.
 3. The module according to claim 1,said at least one element comprising at least two elements, each elementhaving a refractive index that varies between its optical axis or itscentral part and its periphery.
 4. The module according to claim 1,comprising at least a first element comprising a tablet with parallelfaces and a second element comprising an optical lens, at least one ofthe first and second elements having a refractive index that variesbetween its optical axis and its periphery, over at least an annulararea.
 5. The module according to claim 4, wherein said elements haverefractive indices that vary in the reverse direction between theiroptical axis or their central part and their periphery.
 6. The moduleaccording to claim 4, wherein the refractive index of said tabletincreases in a direction between its optical axis or its central partand its periphery.
 7. The module according to claim 4, wherein therefractive index of said lens decreases in a direction between itsoptical axis or its central part and its periphery.
 8. A method offabricating an imaging optical element designed to be placed in front ofan optical image sensor of a semiconductor component and through whichan image is projected towards this optical image sensor, comprising:doping a material forming said element with ions suitable for modifyinga refractive index of the element, such that the refractive index variesbetween its optical axis and its periphery, over at least an annulararea.
 9. The method according to claim 8, further comprising: a previousstep of doping the material forming said element with different ions.10. The method according to claim 8, further comprising: performing anadditional doping of the material forming said element with preliminarydoping ions or with other ions.
 11. The method according to claim 8,wherein said element is made of glass and the doping ions are chosenfrom a group consisting of sodium, potassium, lithium, silver, cesiumand thallium ions.
 12. The method according to claim 8, furthercomprising: doping with thallium ions an element made of glass which waspreviously doped with sodium ions.
 13. The method according to claim 8,further comprising: doping with sodium ions an element made of glasswhich was previously doped with thallium ions.
 14. The method accordingto claim 8, wherein doping comprises: forming on said element a maskhaving at least one annular aperture and/or a central aperture; dopingthe material forming this element through this mask; and removing saidmask.
 15. The method according to claim 8, wherein doping comprises:making crossed grooves in a front face of a wafer so as to formprotruding blocks; forming a mask covering the rear face of said wafer,the end faces of said blocks and the bottom of said grooves; doping withions the material forming said wafer through said mask, radiallyproducing a doping of each of said blocks; and removing said mask. 16.The method according to claim 8, wherein doping comprises: forming on afront face of a wafer a mask comprising, over areas of this front face,a central aperture and/or at least one annular aperture; forming a maskcovering the rear face of said wafer; doping with ions the materialforming said wafer through said mask; and removing said masks.
 17. Anoptical semiconductor package comprising: a semiconductor componentcomprising an optical image sensor on its front face, an imaging opticalmodule placed in front of the optical image sensor of the semiconductorcomponent and through which an image is projected towards this opticalimage sensor, said imaging optical module comprising at least oneelement which has a refractive index varying between its optical axisand its periphery, over at least an annular part.
 18. The opticalsemiconductor package according to claim 23, wherein the refractiveindex of said element varies by increasing in one direction.
 19. Theoptical semiconductor package according to claim 23, wherein saidimaging optical module comprises at least a first element comprising atablet with parallel faces placed in front of the semiconductorcomponent and a second element comprising an optical lens placed infront of said tablet, wherein a diaphragm is inserted between saidtablet and said lens, at least one of these elements having a refractiveindex that varies between its optical axis and its periphery, over atleast the annular area.
 20. The optical semiconductor package accordingto claim 19, wherein said elements have refractive indices varying inthe reverse directions between their optical axis or their central partand their periphery.
 21. The optical semiconductor package according toclaim 19, wherein the refractive index of said tablet increases in adirection between its optical axis or its central part and itsperiphery.
 22. The optical semiconductor package according to claim 19,wherein the refractive index of said lens decreases in a directionbetween its optical axis or its central part and its periphery.
 23. Awafer comprising a multiplicity of parts respectively forming imagingoptical elements designed to be placed in front of optical image sensorsof semiconductor components and through which images are projectedtowards these optical image sensors, each element having a refractiveindex that varies between its optical axis and its periphery, over atleast an annular part.
 24. The wafer of claim 23 wherein the elementscomprise one of tablets or lenses, said tablets and lenses havingrefractive indices which vary in reverse directions between theiroptical axis or their central part and their periphery.
 25. A method offabricating optical semiconductor devices, comprising: forming a firstwafer comprising a multiplicity of parts respectively forming imagingoptical tablets, each tablet having a refractive index that varies in afirst lateral direction from its optical axis towards its periphery;forming a second wafer comprising a multiplicity of parts respectivelyforming imaging optical lenses, each lens having a refractive index thatvaries in a second lateral direction from its periphery towards itsoptical axis; joining together the first and second wafers so that saidtablets and said lenses are placed one on top of the other and compriseimaging optical modules; joining to each optical module a semiconductorcomponent including an optical image sensor; and sawing said joinedwafers so as to cut out a multiplicity of individual semiconductordevices.